The present invention relates to a laser oscillating apparatus which generates laser light by exciting a laser gas by an electromagnetic wave and resonating generated plasma light, and more particularly, to a laser oscillating apparatus using a microwave as an electromagnetic wave for laser gas excitation, an exposure apparatus having the laser oscillating apparatus, and a device fabrication method.
Recently, a so-called excimer laser has attracted attention as the only high-output laser that oscillates in the ultraviolet region, and a wide range of applications of the excimer laser can be expected in the electronic industry, chemical industry, energy industry and the like, specifically, in the processing of and in chemical reactions with metals, resins, glass, ceramics, semiconductors and the like.
The principle function of an excimer laser oscillating device will be described. First, a laser gas such as Ar, Kr, Ne, He, F2 and the like filled in a laser chamber is excited by electronic-beam emission, electric discharge or the like. At this time, the excited F atoms are combined with inert Kr and Ar atoms in a ground state, generating molecules KrF* and ArF* which exist only in an excited state. The molecules are called excimers. The excimers, which are unstable, immediately emit ultraviolet light and dissociate to the ground state. The excimer laser oscillating device utilizes the ultraviolet light emitted from the excimers. The device amplifies the ultraviolet light in an optical resonance device comprising a pair of reflection mirrors as light having a regulated phase, and outputs the light as laser light.
Upon excimer laser-light emission, as well as the above-described electronic beam and electric discharge, a microwave is used as a laser-gas excitation source. The microwave is an electromagnetic wave having an oscillation frequency within a range from several hundred MHz to several ten GHz. In this case, a microwave is introduced from a waveguide via a gap (slot) formed in a waveguide wall into a laser tube, to excite the laser gas in the laser tube into a plasma state.
However, even if the intensity distribution of the microwave emitted from the slot is uniform, in order to supply the microwave in a long space filling the length of the laser-light resonance device, it is necessary to form a slot array structure where plural slots are arrayed along the lengthwise direction of the resonance device. FIG. 9 shows this structure. Plural minute gaps (slots) 202 are formed at equal intervals in a waveguide wall 201. The microwaves are emitted from the minute gaps (slots) 202. In FIG. 9, discharge space within the laser tube is omitted for the sake of convenience.
In use of the slot array structure, an area between adjacent slots 202 (a hatched elliptic portion in FIG. 9) is a microwave non-emitted area. Accordingly, when the laser gas existing in the discharge space is excited by the microwave, the intensity of the microwave has unevenness due to the existence of the microwave non-emitted area, which causes plasma discharge having nonuniform distribution.
The present invention has been proposed to solve the above-described conventional problems, and its object is to provide a laser oscillating apparatus which realizes entirely uniform plasma discharge along a lengthwise direction of a laser tube, and enables laser light emission with minimum energy loss, having a structure which can be very easily designed, a high-performance exposure apparatus having the laser oscillating apparatus, and a high-quality device fabrication method using the exposure apparatus.
According to the present invention, provided is a laser oscillating apparatus for exciting a laser gas by an electromagnetic wave and resonating generated plasma light so as to generate laser light, wherein a light emission portion of the plasma light is a slit-shaped gap formed along a lengthwise direction of a plate member provided above and away from an electromagnetic-wave emission source.
The laser oscillating apparatus further comprises a shielding structure having a shielding wall covering the electromagnetic-wave emission source, wherein the shielding structure is internally supplied with the laser gas, and an upper surface of the shielding structure is used as the plate member, and the gap is formed along the lengthwise direction of the plate member.
In the laser oscillating apparatus, the shielding structure comprises a pair of chambers communicating with each other via the gap.
In the laser oscillating apparatus, the electromagnetic-wave emission source is provided in each of the chambers.
In the laser oscillating apparatus, a waveguide comprising a pair of chambers internally supplied with laser gas is provided above and below the plate member via the gap, and the electromagnetic wave is generated in one of the chambers and is propagated to the other one of the chambers through the gap, to continuously cause the plasma light over the entire area along the lengthwise direction where the gap is formed.
In the laser oscillating apparatus, an end of one of the pair of chambers is shifted to that of the other one of the chambers by a predetermined distance.
In the laser oscillating apparatus, an opening of the electromagnetic-wave emission source is wider than the slit-shaped gap provided above the opening.
Further, according to another aspect of the present invention, provided is a laser oscillating apparatus for exciting a laser gas by an electromagnetic wave and resonating generated plasma light so as to generate laser light, comprising a waveguide comprising a pair of chambers each internally supplied with the laser gas, wherein the waveguide has a slit-shaped gap in a lengthwise direction, and the chambers communicate with each other via the gap, and wherein the electromagnetic wave is generated in one of the chambers and is propagated to the other one of the chambers through the gap, to continuously cause the plasma light over the entire area along the lengthwise direction where the gap is formed.
In the laser oscillating apparatus, an end of one of the pair of chambers is shifted to that of the other one of the chambers by a predetermined distance.
In another aspect of the present invention, in the laser oscillating apparatus, the laser gas is supplied in a flow direction orthogonal to a generation direction of the laser light and across the gap.
In the laser oscillating apparatus, the laser gas is supplied in a flow direction orthogonal to a generation direction of the laser light and across the gap.
In the laser oscillating apparatus, the electromagnetic wave is a microwave.
Further, according to the present invention, in the laser oscillating apparatus, the laser gas is at least one inert gas selected from Kr, Ar, Ne, and He or a gaseous mixture of the at least one inert gas and an F2 gas.
Further, according to another aspect of the present invention, provided is an exposure apparatus comprising: the above laser oscillating apparatus as a light source that emits illumination light; a first optical unit that irradiates a reticle, where a predetermined pattern is formed, with the illumination light from the laser oscillating apparatus; and a second optical unit that irradiates an irradiated surface with the illumination light via the reticle, wherein the predetermined pattern on the reticle is projected on the irradiated surface upon exposure of the irradiated surface.
Further, according to another aspect of the present invention, provided is a device fabrication method comprising: a step of applying a photosensitive material to an irradiated surface; a step of exposing the irradiated surface coated with the photosensitive material via a predetermined pattern by using the above exposure apparatus; and a step of developing the photosensitive material exposed via the predetermined pattern.
In the device fabrication method, the irradiated surface is a wafer surface, and wherein a semiconductor device is formed on the wafer surface.
In the laser oscillating apparatus of the present invention, the electromagnetic-wave emission source and the plasma emission portion (slit-shaped slot) are separately defined, and can be independently designed. Accordingly, if the electromagnetic-wave emission source and the light emission portion are designed to be a predetermined distance away from each other, an electromagnetic wave emitted from the emission source has a plane wavefront near the emission portion, i.e., has an entirely approximately plane wavefront. Accordingly, in the emission portion, as the laser gas is excited by the electromagnetic wave having the approximately plane wavefront, plasma discharge uniform along the lengthwise direction is enabled, and uniform laser light emission can be realized.
The laser oscillating apparatus of the present invention has a waveguide comprising the pair of chambers above and below a slit-shaped gap formed along the lengthwise direction (laser light generation direction), and the gap functions as the electromagnetic-wave emission source and the plasma light emission portion. In this case, when the electromagnetic wave (microwave) is generated in one of the chambers, the electromagnetic wave exists in a standing wave state in the chamber, and in correspondence with the standing wave, plasma discharge is performed with especially large emission light quantity in a position corresponding to the antinode of the standing wave. At this time, in a position where the plasma density is low, i.e., a position corresponding to the wave node of the standing wave, the electromagnetic wave enters the other chamber through the gap. If the other chamber is designed to invert the distribution of the standing wave, plasma discharge is performed such that the plasma density becomes the highest in a position through which the electromagnetic wave is transmitted. That is, in this case, the plasma discharge from the other chamber is performed self-consistently such that a high density position interpolates a low density position in the former chamber. Accordingly, plasma light occurs continuously over the entire space (along the entire lengthwise direction), and uniform laser light emission can be realized.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.